Hi all As long as I can remember I have had this problem, both with my 3,1 and my 4,1 despite doing a fresh install on the latter. I have read around a lot and believe it is something to do with SSD drives in the Mac Pro and lack of temp sensor or something? I have used Crucial M4 and SSD 830 Samsung as boot drives. The drives have been in the first sled bay as well as the CD/DVD bay. I have tried PRAM/SMC Resets with no luck. I just really need help because I am going way in a day or so for quite some time and I wanted to use 'back to my mac' but don't want to leave the fan running on full while I am away! I never reset or sleep the computer in the fear that the fan will be on full when it boots back up. The only thing that helps so far as a a temporary fix is unplugging the power lead before booting, or when the computer wakes from sleep if I sleep it immediately then re-wake it it is fine but obviously can't do this from the other side of the globe!